Next data indicator handling

ABSTRACT

A method and apparatus for a base station engaging in transmissions via at least a media access layer with a user entity are disclosed. The base station transmits data to the user entity over a high speed scheduling and packet data scheduling channels. The base station has a plurality of hybrid automatic repeat request (HARQ) entities cooperating with a scheduler for transmitting frames from at least the base station to the user entity for a given HARQ process. Each HARQ entity receives either a not acknowledge or an acknowledge signal or detects a discontinuous transmission for a given HARQ process. The base station transmits a next data indicator to the user entity. The user entity has at least one buffer associated with a given HARQ process. The buffer stores and performs incremental combining of received data relating to data from the base station. The buffer is capable of being flushed.

FIELD OF THE INVENTION

The present invention relates to packet data traffic and signalingbetween a user entity (UE), a radio base station (Node-B) and a radionetwork controller (RNC). More particular the invention pertains toHSPDA (High Speed Packet Data Access) traffic making use of among othersthe MAC-hs (Medium Access Control High Speed) and RLC (Radio LinkControl Layer) data transmission protocols.

BACKGROUND OF THE INVENTION

HSPDA provides high speed downlink access from an UMTS base station(Node B) to a plurality of user entities by flexible allocation ofdownlink resources.

In prior art document WO2005/034418 FIG. 3, the protocol layers involvedin the communication between user entity (e.g. mobile station), Node B(base station), RNC (implemented by parts CRNC, and SRNC) are shown. Theuser entity involves the following layers: PHY (physical layer), MAC-hs(HSPDA Media Access Control layer), MAC_d (Medium Access Control Device)RLC (Radio Link Control layer). Node B communicates via the MAC-hs layerwith the user entity and via a frame protocol HS_DSCH-FP with the RNC,respectively.

According to the HSPDA specifications, the RLC operates above the MAC-hsprotocol in the protocol stack. The RLC layer provides the connection toupper communication layers such as TCP/IP, both in the user entity andthe RNC. Both the RLC protocol and the MAC-hs protocol are ARQ(Automatic Repeat Request) protocols featuring retransmissions ofincorrectly received protocol data units.

As the name implies, the High Speed Downlink Packet Access (HSDPA)technology provides substantial data capacity advantages. The technicalspecification 3GPP TS 25.321 concerns the MAC (Media Access Control)architecture and the various entities from a functional point of view.3GPP 25.211 basically describes how information from the MAC-layers ismapped onto the channels sent out on the air.

In contrast with release 99 (GSM/EDGE) which exclusively defineschannels between the RNC and the UE, HSPDA introduced the HS-DSCH (HighSpeed Dedicated Shared Channel) channel which is terminated between theuser entity and the base station set (NODE B) also denoted Node B. TheHSPDA Medium Access Control (MAC-hs) enables increased packet datathroughput due to link adaptation (Adaptive Modulation Coding—i.e. 16QAMor QPSK) and fast physical layer retransmission combining. Hence,besides incorporating the WCDMA access technology, Node B carries outscheduling and Hybrid Automatic Repeat Request (H-ARQ) retransmissionson the channel between the user entity and Node B. The benefits and thefeatures of the above system have for instance been described in “WCDMAevolved—High Speed packet data services”, by Stefan Parkwall et al.,Ericsson review No. 2, 2003.

The HSPDA transmission makes use of a 2 ms transmission time interval(three time slots).

On the downlink side, see FIG. 1, there is provided: Several common datachannels 1, a Downlink Physical Channel (DPCH-R99) dedicated signalradio bearer 2 for each user entity using HSPDA transmissions; a commonHigh Speed Shared Control Channel (HS-SCCH) for control signalling 3, anumber of High Speed-Physical Downlink Shared Channels (HS-PDSCH) commonuser data channels 4-5, which are allocated HSPDA data in a flexiblemanner.

On the uplink side, see also FIG. 1, there is provided: a HighSpeed-Dedicated Physical Control Channel (HS-PDCCH) 6—for, among otherthings, providing channel quality information, CQI, and HSPDA automaticrequest signalling—and an uplink dedicated channel associated with eachHSPDA user comprising control information and data, 7.

HSDPA (High Speed Downlink Packet Access) facilitates high speedtransmission on the downlink from Node-B and to the user entity (UE).Under HSPDA, Node-B buffers incoming downlink end-user data and utilisesan internal scheduling entity to determine on which particular channeland when to transmit buffered data according to a scheduling routine. Toaim in the scheduling decision, Node-B continuously receives channelquality estimates from the UE entities. Node-B also has knowledge aboutUE receive capabilities.

Node-B can transmit MAC-hs PDUs (Media Access Control High SpeedProtocol Data Units) to the UEs at a pace of up to 500 times per second.At each 2 ms transmit opportunity (TTI transmit time interval) Node-Bcan vary the MAC-hs PDU size depending on the buffered amount of data,the channel quality estimates, the UE capabilities and the grantedamount of downlink codes available. MAC-hs data for 1 UE up to 4 UEs canbe scheduled at each 2 ms transmit opportunity utilising code division(WCDMA) among the scheduled UEs.

The UE decodes the HS-SCCH (High Speed Shared Control Channel), and upona successful CRC checksum the UE continues to decode the HS-PDSCH (HighSpeed Physical Data Shared Channel). Depending on the outcome of theHS-SCCH and HS-PDSCH, the UE transmits a reception feedback back to thepeer Node-B.

The reception feedback is interpreted by the Node-B transmitter, whichupon a negative feedback or absence of feedback (DTX) indicating apossible reception failure for the UE, retransmits data.

According to specification 3GPP 25.321 chapter 11.6.1 and 11.6.2, thereis utilized a HSPDA N-channel stop and wait (SAW) ARQ, implying that anumber of 1-8 HARQ processes may exist at a time per user entity. Thetiming relation between the downlink HS-DPCCH channel and the uplinkACK/NACK transmissions on the HS-PDSCH are fixed, that is, the ACK, NACKmessages are arranged to be transmitted, such that there are always7.5-9.5 TTI slots between a transmission and the associated expectedACK/NACK from a user entity. This allows for Node-B to easily determinewhen to retransmit data in the case of a missing response to a firsttransmission. The 8 HARQ processes mentioned above reassure that Node-Bmay always utilise a subsequent DPCH slot for transmission to a specificUE either with a retransmission of previously sent MAC-hs data, or for anew MAC-hs transmission.

Base Station and User Entity

In FIGS. 5 and 6, diagram of a base station set (Node B) and a userentity (UE), respectively, are shown.

The base station set, node B, 50, comprises a scheduler, 52, a number ofinput buffers, 53, 54, storing segments of data streams pertaining toindividual user entities, UE1-UEn. For each UE a HARQ entity 55, 56 eachcomprising a number of HARQ processes for handling simultaneoustransmissions to several UE's, that is, for each user entity as well,Layer 1 processing means 57 for transferring data from respective HARQprocesses. The base station moreover comprises a CQI decoder, 58, a userentity (UE) feedback decoder 59 and a layer 1 receiver, 60.

Each HARQ process 55, 56, in a given user entity is mirrored in Node B,and corresponds to a given data stream which is received by a particularuser entity. As explained above, more data streams may be used by theuser simultaneously corresponding to one application or moresimultaneous applications running on the user entity apparatus, possiblywith different QoS requirements. Moreover, consecutive data may betransmitted for the same user entity, the consecutive transmissionbelonging to different HARQ processes.

Moreover, Node B comprises at least one specific input buffer queuededicated to a corresponding set of HARQ processes.

In FIG. 6, a user entity (MAC) 30 arrangement according to the inventionis shown comprising HS-SCCH decoding means, 33, for decoding thedownlink HD-PDSCH channel, arrangements consisting of a number J of HARQprocesses, 36, a number M of reordering and disassembly queues, 39, anda RLC (Radio Link Control) layer means 31. Moreover, there is providedUE (User Entity) feedback processing means, 38, and layer 1 processing,37, for providing feed-back on the HS-DPCCH channel. Finally buffermeans 35 are provided for each HARQ process 36. The buffer means may bearranged as one resource or buffer 35 a plurality of resources orbuffers. The buffer may be arranged as a soft memory which ispartitioned across the HARQ processes in a semistatic fashion throughupper layer signalling. Node B should take into account the UE softmemory capability when selecting transport formats for transmission andretrans-mission and selecting redundancy versions.

The reordering queue distribution function, 39, routes the MAC-hs PDU'sto the correct reordering buffer based on a Queue ID. The reorderingentity reorders received MAC-hs PDU's according to the received TSN(transmit sequence number). MAC-hs PDU's with ascending TSN's (MAC hsTransmit Sequence Numbers) are delivered to the disassembly function. Torecover from erroneous conditions when MAC-hs PDU are missing the sameavoidance handling as described in 3GPP TS 25.321-11.6.2, re-orderingrelease timer and window based stall avoidance, is used. There is onereordering entity for each Queue ID configured at the UE. Thedisassembly entity is responsible for the disassembly of MAC-hs PDU's.When a MAC-hd header is removed, the MAC-d PDU's are extracted and anypadding bits are removed. Then the MAC-d PDUs are delivered to thehigher (RLC) layer. These features have been described in 3GPP TS25.321-11.6.2.3.

The RLC Layer

The RLC layer in 3GPP can operate in three modes, transparent mode,unacknowledged mode and acknowledged mode (AM), which will be focusedupon in the following.

In AM mode, incorrectly received PDU's (Protocol Data Units) discoveredby the receiving side are effected to be retransmitted by thetransmitting side by means of an ARQ (Automatic Repeat Request)protocol.

An AM RLC entity consists of a transmitting side, and a receiving side,where the transmitting side of the AM RLC entity transmits RLC PDU's andthe receiving side of the AM RLC entity receives RLC PDU's.

An AM RLC entity resides in the UE (user equipment) and in the RNC(radio network control), respectively. The transmitting side segmentsand/or concatenates RLC SDU's (service data units) into PDU's of a fixedlength. The receiving side reassembles received PDU's into RLC SDU's andtransmits these to higher data layers. Likewise, SDU's are received fromthe layer above the RLC layer. In AM mode, the RLC layer is responsiblefor the delivery of SDU's in consecutive order.

In FIG. 4 of the above document WO2005/034418, an implementation of theacknowledged mode (AM) UE (base station)/UTRAN (Radio access node/basestation (Node B)) entity is shown.

To facilitate the in-sequence delivery, each RLC PDU is given a sequencenumber, 0-4095, whereby the transmitter transmits PDU's with increasingsequence number modulo 4096. Using the sequence number, the receiver candetect a missing PDU. The receiver can be configured to transmit aSTATUS message upon the detection of a missing PDU. The STATUS reportmay contain positive or negative acknowledgement of individual RLC PDU'sreceived by the peer RLC entity. The transmitter can also request aSTATUS messages from the receiver by setting a Poll flag in the PDUheader. The conditions for that the transmitter sets the Poll flag areamong others:

-   -   Last PDU in Buffer:

When only one PDU exists in the input buffer.

-   -   Poll Timer Expires:

When the timer_poll expires, that is, the transmitter requested a STATUSearlier and initiated a timer_poll to reassure that a response isreceived.

-   -   Window Based Setting:

A transmitter is restricted in the amount of “outstanding data” it cantransmit until a STATUS confirms the reception to the receiving side.“Outstanding data” relates to the earliest unacknowledged PDU.

It should be noted that the above description of the functionality ofthe RLC layer only constitutes a small excerpt of those featuresactually provided.

Selective retransmissions are possible, e.g. if STATUS message indicatesPDU with sequence number (SN) 3, 6 and 13 are missing, only 3, 6 and 13needs to be retransmitted.

MAC-hs Layer

In the following description regarding the MAC-hs layer:

-   -   the MAC-hs transmitter is the Node-B.    -   the MAC-hs receiver is the UE equipment being either a mobile        station or a pc-card attached to a PC or any other equipment        capable of receiving downlink 3GPP HSDPA traffic.

MAC-hs PDU's are numbered by modulo TSN (Transport Sequence Number)cycling through the field 0 to 63.

As mentioned above, the MAC-hs protocol provides multiple Hybrid-ARQprocesses (HARQ) whereby for each HARQ process, the transmittertransmits a MAC-hs PDU and awaits either an ACK indicative of receptionat the receiver or Negative Acknowledgement (NACK) indicative that thereceiver did not receive the MAC-hs PDU or absence of a response (DTX).The round trip time concerning the time from MAC-hs PDU transmissionuntil reception of the feedback (ACK/NACK) is fixed. Upon the receptionof a NACK or DTX, the MAC-hs transmitter retransmits the MAC-hs PDU.Since the round trip time is long in relation to the MAC-HS PDU size andsince multiple users may be adapted to receive packets in timemultiplexed fashion, multiple HARQ processes are provided. If only oneHARQ process was available, the duty cycle (i.e. actual transmissiontime/total possible transmission time) would be low. By using multipleHARQ processes, one HARQ process can await a response, while anotherHARQ process, or multiple HARQ processes, may transmit. Thereby, theduty cycle can be rendered close to 100 percent.

The MAC-hs protocol is semi-reliable, that is, the MAC-hs transmittermay choose to discard or delete a MAC-hs PDU that has been transmittedand possibly been retransmitted to the MAC-hs receiver.

By discarding a MAC-hs for retransmission, unnecessary transmissions areprevented over the radio link in case the MAC-hs receiver has moved toanother cell or has powered down or if the receiver for any other reasonis not capable of receiving data. Therefore, buffered packets arediscarded at the transmitter either at the expiry of a timer set at apredetermined time (e.g. T1) corresponding to the first transmission ofthe packet in question or when a maximum number of retransmissions ofthe packet in question have been performed or based upon a too longwaiting time in the input data buffer, whatever appears first or acombination thereof.

The MAC-hs receiver utilizes a receiver window for the purpose ofmitigating the effect of unnecessary transmissions when PDU's arereceived in non-ascending sequence order (which can occur due toretransmissions). Whenever a MAC-hs PDU is successfully received with aTSN (Transmit Sequence Number) equal to the next expected TSN, thereceiver can deliver PDU's to the RLC layer. Depending on whether thesubsequent TSN number (i.e. next expected TSN+1) has previously beensuccessfully received, that MAC-hs PDU can also be delivered and soforth. The receiver window is updated accordingly. Delivery to the RLClayer from the MAC-hs protocol is done in consecutive order also denotedin-sequence.

To recover from the situation where e.g. the transmitter has discarded aMAC-hs PDU, the receiver utilizes two mechanisms I)+II) to solve theproblem:

I) Timer Based Stall Avoidance:

At the reception of a PDU with TSN>next_expected_TSN the receiver startsa timer denoted T1. When the timer expires, the receiver makes properactions to allow for subsequent PDU's to be received. The exact detailsare described in 3GPP 25.321 Chapter 11.6.2.3.2. The behavior is shownin FIG. 2.

-   At time 1) a PDU with TSN=4 is received, the next expected transmit    sequence number being 3, whereby timer T1 starts.-   At time 2) PDU's with TSN 6 and 7 are received.-   At time 3), the timer expires, whereby TSN=4 is delivered to the RLC    layer. Next expected_TSN=5. A new timer T1 starts since    next_expected_TSN=5 is not received and at least one PDU exists in    receiver window.-   4) TSN 6 and 7 remains in buffer.    II) Window Based Stall Avoidance:

Upon the reception of a PDU with TSN outside the receiver window, thereceiver shall shift its “right” (or “upper”) window edge andhighest_received_TSN to the received TSN. Next_expected_TSN shall beupdated to highest_received_TSN-receiver window size+1 previously PDU'sstored in window that now fall outside the window shall be delivered toRLC layer. This has been illustrated in FIG. 3.

Assume that the receiver window size is of length 8.

-   At time 1) PDU TSN 4 has been received, which is within the receiver    window, TSN=3 is next_expected_TSN, timer T1 is running.-   At time 2) TSN=12 is received, which is outside the receiver window    thus causing the window to advance, the next_expected_TSN is    updated, and PDU TSN=4 is delivered to RLC. A new timer T1 starts    since next_expected_TSN is not received and a PDU exists in the    receiver window.    Further Features of the MAC Layer:    MAC-hs reset:

MAC-hs is used to restart the MAC-hs protocol, where the MAC-hs receiverdelivers stored data in its receiver window to RLC layer and sets itsnext_expected_TSN=0 and highest_received_TSN=63. It is used uponconditions such as handover between cells.

UE Addressing in HS-SCCH:

A UE ID (In 3GPP denoted Radio Network Temporary Identifier (RNTI)) thatidentifies the UE for which the HS-SCCH information is intended isimplicitly included in the CRC (Cyclic Redundancy Check). Whengenerating the CRC checksum in Node-B, the UE ID is included in thecalculation. Upon reception of a HS-SCCH a UE utilizes its ID in thecalculation of the CRC to check whether HSDPA data is destined to theUE.

HS-SCCH Content:

The HS-SCCH has the following content:

-   Transport-Format and Resource-related-Information (TFRI)-   HARQ ARQ-related information such as,    -   HARQ process number    -   Redundancy version (RV)    -   New-Data-Indicator (NDI)        MAC-hs Header Content:

In FIG. 4, a MAC-hs transmission to one HARQ process queue ID, withsequence number TSN, and k different SID (Size Index Identifier) areshown. Either the transmission comprises k different SIDs or less than kif the transmission order is ‘first SID followed by second SID followedby first SID again and so forth’.

Using multiple SID is a mechanism by which higher layer can utilise onesingle MAC-hs queue for transmission of several higher layer priorityqueues, each of which has a specific SID.

Incremental redundancy is used by HSDPA, whereby each HARQ processbuffers previously unsuccessfully received data. The stored informationis utilized in a cyclic redundancy check (CRC) process wherein thestored information and the recent information are combined before beingfed to the decoded of the error-correction code so as to resolve datatransmitted over multiple occasions. Chase combining is considered to bea particular case of Incremental Redundancy. To support the IncrementalRedundancy combining scheme, the Redundancy Version (RV) is signaled inthe HS-SCCH. This process has been described further in 3GPP 25.214.When successfully decoding data, a positive cyclic redundancy checkvalue is formed indicating that data has been correctly received. Whichparticular retransmission method to use is fully determined by theNode-B and is indicated to the UE via the RV in each HS-SCCH in eachTTI.

The new data indicator flag according to 3GPP 25.321 is used by Node Bas an indication for the user entity. According to 3GPP the conditionsfor operating the NDI is specified as follows:

-   -   The HARQ process sets the New Data Indicator (NDI) in        transmitted MAC-hs PDUs. UTRAN should:        -   set the New Data Indicator to the value “0” for the first            MAC-hs PDU transmitted by a HARQ process;        -   not increment the New Data Indicator for retransmissions of            a MAC-hs PDU;        -   increment the New Data Indicator with one for each            transmitted MAC-hs PDU containing new data.

According to 3GPP 25.321 it is noted that the scheduler may re-use TSNsby toggling the NDI bit in order to resume pre-empted transmissions orto force the UE to flush the soft buffer. In this case the content ofthe payload may be changed but care should be taken to preserve thehigher layer data order.

3GPP does not specify the HARQ process behavior upon a successfuldecoding of MAC-hs, which opens up for two possible alternatives for aUE manufacturer:

To flush, i.e. to delete, the stored HARQ process information (UEbehavior 1).

The benefit of this behavior is that the HARQ process can be independentof the NDI setting in subsequent MAC-hs transmission, i.e. to acceptboth an incremented and a non-incremented NDI.

The drawback of this behavior will occur when the acknowledgementtransmitted back to the Node-B fails, and Node-B retransmits the MAC-hstransmission. Note that the MAC-hs has already been delivered to thereordering entity so that is not a problem, but the problem lies in thefact that unnecessary MAC-hs transmissions may occur and an increasedrisk of stalling the Node-b sender.

To store the HARQ process information (UE behaviour 2).

To store the HARQ process information will mitigate the effect of thebehavior (UE behavior 2) above when a Node-B fails to decode atransmitted ACK. In the following it is assumed that the prior art userentities stores buffer information until for example an NDI indicationis received.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows channels according to HSPDA

FIG. 2 shows a known MAC-hs procedure for timer based stall avoidance,

FIG. 3 shows a known procedure for window based stall avoidance,

FIG. 4 shows the known MAC-hs header structure,

FIG. 5 shows a base station implementation according to the prior artand a first embodiment of the invention,

FIG. 6 shows a user entity implementation according to the prior art anda first embodiment of the invention,

FIG. 7 shows a known scheduling HARQ process interaction state diagram,

FIG. 8 shows first embodiment of base station functionality according tothe invention,

FIG. 9 shows first embodiment of user entity functionality according tothe invention,

FIG. 10 discloses a scenario over a imperfect radio interface for priorart devices,

FIG. 11 discloses a scenario over an imperfect radio interface for atleast a first embodiment of a base station according to the invention,and

FIG. 12 shows a second embodiment of user entity functionality accordingto the invention.

SUMMARY OF THE INVENTION

It is a first object of the invention to overcome the problem oferroneous incremental buffer operations in a receiver.

This object has been accomplished by the method for transmitter entityspecified in claim 1 when operating with user entities having a givenbehavior in which buffer values are stored, wherein the transmitterentity carries out the steps of

-   -   awaiting a scheduling instruction or scheduling of download        data;    -   if the outcome from previous media access transmission or        transmissions is detected as a discontinuous transmission (DTX)        setting the next data indicator (NDI) to the value previously        used,    -   otherwise toggling the next data indicator value;    -   transmitting data for the given hybrid automatic repeat request        (HARQ) process.

This object has moreover been accomplished by the transmitter entityspecified in claim 5 even when operating with known user entities havinga given behavior.

It is a further object to set forth improvements for the user entitywith regard to efficient handling of data in buffers.

This object has been accomplished by the method defined in claim 2,wherein the method comprises the steps of—starting a timer whenever datafrom the base station (Node B) is correctly decoded over a HS-SSCHchannel for a given HARQ process;

-   -   if the timer expires without any subsequent data is being        correctly decoded over the HS-SCCH channel for the given HARQ        process;        flushing the content of stored HARQ information for the given        HARQ process.

Further aspects have been accomplished by method claim 3 and the userentities defined in claims 7 and 8, wherein

Further advantages will appear from the following detailed descriptionof the invention.

DETAILED TECHNICAL DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

In FIG. 7, a state diagram pertaining to a given HARQ process in a HARQentity according to the invention is shown. The state diagramillustrates the interaction of a given HARQ process with the Node Bscheduler, which is shown in the implementation shown in FIG. 5.According to FIG. 7, the HARQ process may attain a free state 101, whereno data is assigned for the given HARQ process. When data is handed downfrom the scheduler, 52, for assignment to the HARQ process, the givendata is assigned to the HARQ process for transmission, state 102. Inthis state, the data is buffered and is ready fortransmission/retransmission or discarding depending on the outcome ofthe communication with the interacting receiving side of the HARQprocess, that is, for instance, the user entity as receiving side. Atthe reception of a (re-)transmit message 109 from the scheduler, theHARQ process transmits buffered data. If a NACK is received, or DTX, theprocess remain in state 102 and is ready for a retransmission at thereception of a 109 (re-)transmission signal from the scheduler. After apredetermined number of retransmissions, or dependent upon a too longtime after first transmission, or a combination thereof, or dependentupon reception of a stop signal 106 from the scheduler, a state changefrom state 102—transmitting—to state 103—transmission not ok—isinflicted. If on the other hand an ACK is received, the recenttransmission is deemed to be successful, 104. Since the radio interfaceis prone to interruptions and noise, the received messages may notnecessarily correspond to the messages transmitted from the receiver.The scheduler interacts with the HARQ process, either when new datashould be assigned, i.e. new data is handed down, message 108 or whenforcing the HARQ process to stop, 106, and when a transmission orretransmission shall occur 106. The HARQ process in turn, signals theavailability of transmission resources in the process as a feed requestsignal, 107. The scheduler may order the entity to stop anytransmission, due to indications from higher higher layers, i.e. RLC,indications or power limit considerations etc.

Node-B can determine when an UE transmitted a feedback upon a MAC-hstransmission. 3GPP specifies the exact timing to be used and both ACKand NACK are explicitly signaled from the UE. A NACK is signaled fromthe UE when it successfully decodes the HS-SCCH but fails to decode theHS-PDSCH. When the UE fails to decode the HS_SCCH nothing will betransmitted from the UE and Node-B will interpret this as a DTX andinitiate a retransmit procedure. Note that DTX can also be detected dueto poor uplink radio conditions.

In FIG. 8, a flow diagram pertaining to a given HARQ process of a givenHARQ entity in Node B communicating is shown.

In step 0 the HARQ process is waiting for the scheduler to hand downinstructions or downlink data. In step 1, the process is evaluatingwhether the outcome from a previous MAC_hs transmission or previoustransmissions were evaluated with a DTX finding by node B, hence that,neither a NACK nor an ACK was received by node B for the correspondingHARQ process reply. If the answer is yes, the NDI is set such as theprevious NDI value pertaining to the HARQ process is used, and if theanswer is no, the NDI value is toggled or changed in relation to therecent used NDI vale for the HARQ process. Accordingly in step 4, aMAC_hs packet is transmitted for the given HARQ process with the NDIvalue set as defined above.

In other words there is provided a method for a base station (50)engaging in transmissions via at least a media access (MAC) layer with auser entity (30); wherein

-   -   the base station is transmitting data to the user entity over a        high speed scheduling channel (HS-SCCH) and a high speed packet        data scheduling channel (HS-DPCCH); the base station (50) having        a plurality of hybrid automatic repeat request (HARQ) entities        (55, 56) cooperating with a scheduler (52) for transmitting        frames from at least the base station (50) to the user entity        (30) for a given hybrid automatic repeat request process, each        hybrid automatic repeat request (HARQ) entity being adapted for        receiving either a not acknowledge signal (NACK) or an        acknowledge signal (ACK) or detecting a discontinuous        transmission (DTX) for a given hybrid automatic repeat request        (HARQ) process, the base station (50) being adapted for        transmitting a next data indicator (NDI) to the user entity        (30);    -   the user entity (30) having at least one buffer (35) associated        with a given HARQ process, the buffer being adapted for storing        and performing incremental combining of received data relating        to data from the base station (50), the buffer moreover being        adapted for being flushed,    -    the method comprising the steps of        -   awaiting a scheduling instruction and scheduling of download            data (0; 108, 109);        -   if the outcome from previous media access transmission or            transmissions is detected as a discontinuous transmission            (DTX) setting the next data indicator (NDI) to the value            previously used (3),    -   otherwise toggling the next data indicator value (NDI)(2);        -   transmitting data for the given hybrid automatic repeat            request (HARQ) process.

The base station carrying out the above steps corresponds to the oneshown in FIG. 5, having regard to the state diagram of FIG. 7.

In FIG. 10, an exemplary scenario for the communication between a priorart Node B and a prior art user entity (behavior 2) is given.

The HARQ process in the HARQ entity is shown consisting of 6 HARQprocesses, which is normally the case, keeping in mind that up to 8 HARQprocesses are possible. In the present example we shall only study HARQprocess number 2, although the other 5 processes have been indicated butnot further specified for putting the example into perspective. Itshould be noted that the timely response from the user entity, beingeither a NACK or an ACK or the perception in node B of a lackingresponse, i.e. DTX, can not be inferred from the figure.

A given MAC_hs packet comprising a payload having a MAC_hs transmitsequence number (TSN) 10 is attempted transmitted at the outset, step 2.The NDI value is set by default to the value 0 (TX NDI), this valuebeing perceived by the receiver (RX NDI). Consequently, the receiverstores data pertaining to TSN 10 in its HARQ process buffer. On findingthat the CRC value which is subject to the incrementally processing asdescribed in connection with the prior art is not OK, step 5, a NACK istransmitted to Node B in step 6.

Node B performs a retransmission of the data pertaining to TSN 10, NDIflag transmitted and perceived by the receiver is 0, step 8. Thereceiver performs incremental combining of its buffer for datacorresponding to TSN 10. This time the cyclic redundancy check ispositive, step 11. An ACK is therefore transmitted back to thetransmitter, in step 12, while for security reasons the receiver keepsthe obtained buffer value, confer user entity behavior 2 above.

Next, the transmitter proceeds to transmitting TSN 16, by example, instep 14. According to the 3GPP specification, Node B, toggles NDI tovalue 1, for indicating that new data corresponding to TSN 16 isunderway to be processed.

In the present scenario, the receiver fails to receive the transmissionin step 14, and has therefore no perception of the NDI value. It is notreceived. No response is given by the receiver, and the transmitterperceives the lacking response for HARQ process 2 normally due at thesame time as HARQ process 6 as discontinued transmission, DTX.

A retransmission is attempted in step 20 without success. Consequently,the transmitter discards TSN 16 in step 23.

In step 26, a new TSN 20 is transmitted while toggling NDI to attain thevalue 0.

Since the receivers' perception of last NDI value was 0, the receiverperforms incremental combining with TSN 10 and 20, which will provide anegative CRC value although the transmission was received correctly. Thereceiver transmits a NACK to the transmitter, step 30. Consequently,step 32, TSN 20 is retransmitted.

In FIG. 11, an exemplary scenario for the communication between a Node Baccording to the invention arranged to function as discussed in respectof the flow diagram of FIG. 8 and a prior art user entity (behavior 2)is given. The scenario is also valid for communication between a Node Baccording to the invention and to a first and to a second embodiment ofan improved user entity according to the invention (specified later).The signaling over the radio interface (faulty signaling over the radiointerface) is corresponding closely to the scenario given in FIG. 10, sothat the differences in handling will be demonstrated.

As appears from FIG. 11, the events corresponding to steps 1-20, areidentical to those of FIG. 10. However, in step 26, Node B, according toroutine step 1, in FIG. 8—outcome from previous MAC-hs transmissiondeemed to be an interrupted transmission, DTX—is answered yes—since thiswas the case in step 26, FIG. 11, Node B uses the previous NDI as statedin routine step 3 of FIG. 8.

A prior art user entity according to behavior 2 (and for behavior 1 forthat matter) will flush its buffer 35 and subsequently incrementally addthe empty buffer (0) with data for TSN 20. If data is intact after thetransmission, the CRC will provide a positive value and the user entitywill provide an ACK in step 30. Node B will be ready to transmit newdata of e.g. TSN 25 in step 32. It appears that the efficiency of thetransmission is enhanced in relation to the scenario of the prior artgiven in FIG. 10.

According to the invention the performance of the user entity can alsobe improved.

In FIG. 9 a first embodiment of a user entity adapted for co-operatingwith the first embodiment of the Node B according to the invention (orto a Node B according to the prior art) is shown.

As can be understood from above, the User entity (30) is engaging intransmissions via at least a media access (MAC) layer with a basestation (50); wherein

-   -   the base station is transmitting data to the user entity over a        high speed scheduling channel (HS-SCCH) and a high speed packet        data scheduling channel (HS-DPCCH);    -   the user entity engaging in at least one hybrid automatic repeat        request (HARQ) process (36) for receiving frames from the base        station (50);    -   wherein a hybrid automatic repeat request (HARQ) entity in a        base station being adapted for receiving either a not        acknowledge signal (NACK) or an acknowledge signal (ACK) or        detecting a discontinuous transmission (DTX) for a given hybrid        automatic repeat request (HARQ) process, the base station (50)        being adapted for transmitting a next data indicator (NDI) to        the user entity (30);    -   the user entity (30) having at least one buffer (35) associated        with a given HARQ process, the buffer being adapted for storing        and performing incremental combining of received data relating        to data from the base station (50), the buffer moreover being        adapted for being flushed.

According to FIG. 9, the user entity is

-   -   starting a timer (Y) whenever data from the base station        (Node B) is correctly decoded over a HS-SSCH channel for a given        HARQ process (2, 3);    -   subsequently data is added with the contents of the buffer 35        for the given HARQ process, step 4;    -   if the timer (Y) expires, step 6, without any subsequent data is        being correctly decoded, step 5, over the HS-SCCH channel for        the given HARQ process (5, 6); the user entity is flushing the        content of stored HARQ information for the given HARQ process,        step 7.

More specifically, the user entity waits for data from the base station,step 1. If HS_SCCH data is correctly decoded from the base station, step2 it is examined whether the NDI flag has changed from its previousvalue, step 2 a. If that is the case the UE flushes its buffer, step 2b, and if not, step 3, the UE sets a timer Y.

Subsequently, the UE combines the received data with the contents of itsbuffer. A CRC check is made subsequently, if CRC check is positive datais transferred to the reordering entity and if the CRC check isnegative, the process proceeds to step 5, in which subsequent data fromthe base station is awaited.

If data is received in step 5, the process continues in step 2, if notit is investigated in step 6, whether the timer has expired. It thetimer has not expired, the process goes to step 5, and if it has expiredthe buffer is flushed in step 7, after which the routine commences atstep 1 anew.

As an alternative to the method above shown in FIG. 9, is shown in FIG.12 where among other step 2 is modified such that it is investigatedwhether data from the base station (Node B) is correctly decoded overthe HS-SSCH channel for a given HARQ process (2, 3). Moreover, step 5 ismodified such that it is investigated whether subsequent data from thebase station (Node B) is correctly decoded over the HS-SSCH for a givenHARQ process (2, 3).

More specifically, in FIG. 12, in step 1 data is awaited from the basestation. In step 2, it is investigated whether HS_SCCH data and HS-PDSCHfrom the base station is correctly decoded. If this data is correctlydecoded from the base station, step 2, it is examined whether the NDIflag has changed from its previous value, step 2 a. If that is the casethe UE flushes its buffer, step 2 b, and if not, step 3, the UE combinesthe received data with the contents of its buffer, step 4. A CRC checkis made subsequently, 4 a, if the CRC check is positive a timer Y isstarted, 3 and data is transferred to the reordering entity, step 4 b.The process proceeds to step 5, in which subsequent data from the basestation is awaited. If more data is received, it proceeds to step 2, ifnot it is investigated whether the timer Y has expired, step 6; if thisis the case the buffer is flushed, 7, and moves to step 1; if it is notthe case the process moves to step 5.

The effect of the above procedure, FIG. 9 and FIG. 12, is that the UEHARQ process will decode subsequent HS-SCCH/HS-PDSCH transmissionindependent on any earlier transmission, If we consider situations wherethe UE due to an obstacle looses contact with the 3GPP network for aconsiderably longer time than e.g. the T1 timer setting, it is verylikely that the Node B HARQ processes have discarded its MAC-hs PDUcontent. To flush the HARQ processes during such a situation willminimize the risk of combining incorrect (or correct) data from oneearlier MAC-hs PDU with TSN=y with incorrect (or correct) data fromMAC_hs PDU with TSN<>y.

Concerning the probabilities for receiving an ACK, NACK or DTX signal,most transmission will result in a successful decoding in UE andsuccessful reception of the feedback at the Node-B, which is obvious toobtain a good HSDPA throughput. At the cell border, or due to variouskinds of obstacles, the radio signal quality may decrease such thatNode-B fails to receive an ACK upon a MAC-hs transmission. Of coursesituations may occur when the uplink radio quality is poor whilstdownlink radio quality is good, but Node-B will then (normally) startits retransmit procedure and try multiple times. If the uplink radioquality persists to be poor Node-B will detect this and preventsubsequent transmission.

Of course the previous situation may occur during a MAC-hs transmissionbut we think it more likely that both the downlink and the uplink willbe poor simultaneously and this will be the main reason to end up in theproblem scenario addressed in this invention.

At rare occasions, HS-SCCH transmission (-s) will perceive so poor radioquality that none of the repetitions will be successful. When theseoccasions occur our invention will increase the probability for asuccessful outcome for the subsequent transmission.

1. Method for a base station engaging in transmissions via at least amedia access layer with a user entity, comprising: wherein the basestation is transmitting data to the user entity over a high speedscheduling channel and a high speed packet data scheduling channel; thebase station having a plurality of hybrid automatic repeat request(HARQ) entities cooperating with a scheduler for transmitting framesfrom at least the base station to the user entity for a given HARQprocess, each HARQ entity receiving either a not acknowledge signal oran acknowledge signal or detecting a discontinuous transmission for agiven HARQ process, the base station transmitting a next data indicatorto the user entity; the user entity having at least one bufferassociated with a given HARQ process, the buffer storing and performingincremental combining of received data relating to data from the basestation, the buffer more over capable of being flushed, the methodcomprising the steps of awaiting a scheduling instruction and schedulingof download data; if the outcome from previous media access transmissionor transmissions is detected as a discontinuous transmission setting thenext data indicator to the value previously used, otherwise toggling thenext data indicator value; transmitting data for the given HARQ process.2. Base station engaging in transmissions via at least a media accesslayer with a user entity; wherein the base station is transmitting datato the user entity over a high speed scheduling channel (HS-SCCH) and ahigh speed packet data scheduling channel (HS-DPCCH); the base stationhaving a plurality of hybrid automatic repeat request (HARQ) entitiescooperating with a scheduler for transmitting frames from at least thebase station to the user entity, each HARQ entity receiving either a notacknowledge signal (NACK) or an acknowledge signal (ACK) or detecting adiscontinuous transmission (DTX) for a given HARQ process, the basestation transmitting a next data indicator to the user entity; the userentity having at least one buffer associated with a given HARQ process,the buffer storing and performing incremental combining of received datarelating to data from the base station, the buffer moreover capable ofbeing flushed, a respective HARQ entity awaiting a schedulinginstruction and scheduling of download data; if the outcome fromprevious MAC transmission or transmissions is detected as adiscontinuous transmission setting the next data indicator to the valuepreviously used; otherwise toggling the next data indicator value;transmitting data for the given HARQ process.
 3. Base station accordingto claim 2, comprising a scheduler in a base station, a plurality ofinput buffers, a plurality of HARQ entities, each entity comprising HARQprocess means for controlling and performing the transmission of datafor a given HARQ process, the base station furthermore comprising alayer 1 receiver, a CQI decoder and a user entity feedback decoder, thescheduler comprising a processing means for evaluating ACK, NACK and DTXconditions.